heat exchanger welds, 6013, need advice

[VanMarco]

hello there! im building a low pressure heat exchanger similar to a scotch boiler for coal. I have another thread on another forum regarding its design consideration, but, matters not.
Basically, i'm struggling with welding, or more like, achieving better penetration.
Now, i cannot use 6010s as my welder hasnt enough voltage for these. I can only do 6013 and then 7018 cap. Now the weld type will be a pipe sticking out of a hole just some, and the weld would create a nice donut around it.
So far, I've tried different things, the best i could do is 3mm out of 6 of the plate where it's going to be welded.
I used some bevelling and preheating, 6013 / 100A electrode positive.

Here's the pics. Please disregard that nasty stuff on the lower edge, i got my arm hot and moved away badly, i wasnt testing my ability to do the whole ring perfect, thats not an issue. I was testing penetration.
so my question is, do i need to do like, almost all the way down bevelling, fill the bottom with 6013 but without melting the entire pipe into the weld just yet, and then cap with 7018 on top of that?
Pressure involved are low, 0.5 0.6 bar, just enough to keep any air out of the system really.
Thanks

 

[Mikes]

With those low pressures (assuming both pressures are low), I would be more than happy to weld with just a 6013 with one pass and good penetration. Adding a 7018 cap isn't really necessary. Half bevel the plate thickness, 3 mm tube projection and a 3.2 mm good quality rod at about 110 Amp. Sounds like an interesting project.

 

[tom2207]

are you doing them horizontal or vertical ?

 

[knighty]

zooming in, it looks like you've welded around the pipe, instead of welding around the pipe/plate joint?

personally for those, they're both thick enough that I'd mount them flush then weld around the join

having them flush would make it much easier when there's a lot to do because you can weld straight on from the top instead of working round it? - probably easier where there's pipes close together too


when it comes to doing lots of them I'd be tempted to have the plate face down on a flat surface, add the pipes one at a time and tack them on from the back, then flip it over to finish it off (with the other end's plate on the ends of the pipe)

flip it over again to tack a couple of pipes to the other end plate, flip it again and weld that from above

 

[VanMarco]

Mikes, would you say it;s best I use 3.2mm ones instead of over-amp 2.5mm ones given the thickness? (6mm plate, 3.2mm pipes)
Tom will all do these horizontal (flat position)
Knigthy, the assembly will be having two identical 6mm rounds welded onto drum ends (its 5mm thick) then slide all the pipes and tack each on either side, then flip the drum so that i can have the face flat, and weld all, repeat on other side.
I was told that it's best to have these pipes stick out a little and collapse the edge onto the weld puddle, creating that donut-type shape, as this appear to be the strongest.

Also I do know, it would be best to have full penetration, as even though pressure is low, container will range between 20 and 75c, so it's possible overtime welds may crack, yet i am fine with that, my heart tells me it won't crack after just one year

also thanks for your answers!!!

 

[Brad93]

The proper way to prep that tube plate would be with a J prep. This is done with a bevelling machine which which can be hired.

I personally would dispense with a 6013 as you have seen they can be liable to slag inclusions at the beginning of the weld for the inexperienced.

I would go with a 2.5mm 7018 or better yet 7016 such as Filarc 56S or Conarc 49C.

The filarc and conarc have a lighter slag which will not tend to run in front of your weld in a tight bevel.

If you must do 6013 then choose an RC type rod which will be deeper penetrating

 

[VanMarco]

I have also 7018s, both 2.5mm and 3.2mm. I dont know if the 3.2mm are too "hot" maybe?
Also as i was practicing a bit with the plasma and made new test holes, i welded another and this time i just filled the gap and not bothered to make sure the pipe edge would collapse into the puddle, the weld looks better.
As usual disregard the 2 small slag inclusion, thats the 2 tacs that i lazily didnt clean up before welding. yes, lazy me. In proper project I know, clean, and feather dont need to say !

is my technique bad? thanks!!!

 

[Mikes]

Mikes, would you say it;s best I use 3.2mm ones instead of over-amp 2.5mm ones given the thickness? (6mm plate, 3.2mm pipes)
Tom will all do these horizontal (flat position)
Knigthy, the assembly will be having two identical 6mm rounds welded onto drum ends (its 5mm thick) then slide all the pipes and tack each on either side, then flip the drum so that i can have the face flat, and weld all, repeat on other side.
I was told that it's best to have these pipes stick out a little and collapse the edge onto the weld puddle, creating that donut-type shape, as this appear to be the strongest.

Also I do know, it would be best to have full penetration, as even though pressure is low, container will range between 20 and 75c, so it's possible overtime welds may crack, yet i am fine with that, my heart tells me it won't crack after just one year

also thanks for your answers!!!

I only suggest 3.2 mm rods as you have more metal to play with. If you've got enough scrap, give it a go and see which you prefer. Don't think at 75 C you will get any cracking. Hardly hot in the big scheme of things. Intrigued as to what this is going to be for!

 

[VanMarco]

It's a heat exchanger made somewhat like this. it'll be just the drum over my existing firebox, flue gases go through it, heating the water inside.

this is my tank. I am also told I need to have the lids go INSIDE the drum, and not over the edge as it's stronger.

 

[addjunkie]

It is normal in a pressure vesselto have openings oval and fitted on the inside. Stops them blowing off if you get your pressure temperature sums wrong.
What you are i effect building is a fire tube boiler. So you should also have a thermal relief valve / over pressure safety valve fitted, again in case you get your sums wrong. It doesn't take much heat with water to rattle up-the pressure.

It also doesnt take much pressure to make a poorly designed pressure vessel go bang.

 

[VanMarco]

It is normal in a pressure vesselto have openings oval and fitted on the inside. Stops them blowing off if you get your pressure temperature sums wrong.
What you are i effect building is a fire tube boiler. So you should also have a thermal relief valve / over pressure safety valve fitted, again in case you get your sums wrong. It doesn't take much heat with water to rattle up-the pressure.

It also doesnt take much pressure to make a poorly designed pressure vessel go bang.

eheh, yes, i do know about safety valves, don't worry. what you mean by oval and fitted on the inside? you mean the water intake and outtake should be inserted from the inside and welded from the outside, so the lip would prevent it coming off?

 

[denlow60]

hello there! im building a low pressure heat exchanger similar to a scotch boiler for coal. I have another thread on another forum regarding its design consideration, but, matters not.
Basically, i'm struggling with welding, or more like, achieving better penetration.
Now, i cannot use 6010s as my welder hasnt enough voltage for these. I can only do 6013 and then 7018 cap. Now the weld type will be a pipe sticking out of a hole just some, and the weld would create a nice donut around it.
So far, I've tried different things, the best i could do is 3mm out of 6 of the plate where it's going to be welded.
I used some bevelling and preheating, 6013 / 100A electrode positive.

Here's the pics. Please disregard that nasty stuff on the lower edge, i got my arm hot and moved away badly, i wasnt testing my ability to do the whole ring perfect, thats not an issue. I was testing penetration.
so my question is, do i need to do like, almost all the way down bevelling, fill the bottom with 6013 but without melting the entire pipe into the weld just yet, and then cap with 7018 on top of that?
Pressure involved are low, 0.5 0.6 bar, just enough to keep any air out of the system really.
Thanks

Take your pick, you should always lay 2 layers due to leakage.

 

[gaz1]

im going to ask here

you say this is for coal and to my knowledge newcoal isnt that brilliant but still viable

but to note that system that you have chosen isnt the best one to use and it will chug away for fun as its based on a simple design of the steam trains

now i also note that your in my area even though its a big area, playing with a smoking system will catch you plenty of fines

there is better systems out there

 

[Mikes]

Can't see anything about coal. What VanMarco is describing is just an economiser which was sometimes fitted to a boiler to improve overall efficiency. Nothing too special. I think addjunkie is referring to the existing flanged access. As it is being made as a fire tube economiser the flange won't be needed and could be bolted or welded closed. It's going to be trickier to make the flue end covers gas tight and removable for cleaning.

 

[tom2207]

at that size ,,,, why not just take it to someone with a decent mig or tig ,,, do the prep , clean everything well , remove mill scare , bung someone a few quid and the jobs done. There must be plenty of places round that area with lots of experience .

 

[gaz1]

Can't see anything about coal. What VanMarco is describing is just an economiser which was sometimes fitted to a boiler to improve overall efficiency. Nothing too special. I think addjunkie is referring to the existing flanged access. As it is being made as a fire tube economiser the flange won't be needed and could be bolted or welded closed. It's going to be trickier to make the flue end covers gas tight and removable for cleaning.

the coal reference is down to the boiler side of it on the first post

whilst the intention is to put it over an existing firebox whilst also not saying what hes burning

even in that state it would be far better to use the stoves chimney exit at the rear and send it through the tubes and then up the chimney or alternative

you also get a good seal and the tubes become cleanable

 

[addjunkie]

eheh, yes, i do know about safety valves, don't worry. what you mean by oval and fitted on the inside? you mean the water intake and outtake should be inserted from the inside and welded from the outside, so the lip would prevent it coming off?

No, pressure vessel doors for inspection are elliptical or oval in shape, so can be inserted inside and rotated to close up the hole. So as the pressure rises the joint seal improves. Or if external flanges they need to be-the same spec as the rest of the vessel and be able to withstand stand the Maximum allowable working pressure. And should be hydro tested to 150% of MAWP at construction, and 90% of MAWP once safety valves are fitted.

Its about 40 years since Ive welded inside a boiler, and that was an emergency job. But the diagrams above look right for end plate set up.

If the side inspection hole isnt needed weld it up. To seal your tube plates in the exchanger youll need to flange the end, and fix the tube plates between the end cover and the vessel flange. The other end will need to have some allowance for expansion. If its flanged/ fixed at both ends the tubes will be under compression when heating, due to linear expansion.

 

[Brad93]

That's not a heat exchanger that's a boiler!!

 

[VanMarco]

That's not a heat exchanger that's a boiler!!

Im just building the exchanger part. i already have the boiler. We burn mainly lignite, firewood, whatever burns.. issue is, the current boiler is just with some copper pipes and efficiency has been measured at less than 30%. this design is min 60% efficient. also this boiler is outdoors, not indoors. it's to heat the house, water circulating system, not air or anything. Also, money are tight, this already costed over 500 usd in materials, avg. salary here is 250 per month.

the side inspection hole isnt something i fab, it was the tank made like such. I don't need and it'll be welded.

So what denlov was saying is that i need to have two layers of weld on each pipe and not just one go?

Also ty so much, you all been so helpful

Ah yes, sorry, I didnt notice my profile wasnt updated, i do live in romania, sorry about that!!

 

[chrismac]

So what denlov was saying is that i need to have two layers of weld on each pipe and not just one go?

Its belt and braces, sould there be a pore in the root run, the capping run will seal it, I would also agree with the pipe either set under flush or through as then its fillet welds in the diagrams above, they are better than unpreped flush joints to be welded.